In medical diagnosis and therapy, open surgical operations are being replaced to an increasing extent by the use of endoscopes. However, flexible glass fibre endoscopes become massively infected with microorganisms which are present in body cavities, on the mucous membrane, and in the blood. Accordingly, used endoscopes have to be thoroughly cleaned and disinfected after each use.
Glass fibre endoscopes are extremely complicated precision instruments which have moving parts and which are made from a number of materials. They are extremely difficult to clean and disinfect for a number of reasons. Not only the outer surfaces of the instrument, but also the narrow bores present in the interior have to be cleaned and disinfected. In view of the sensitivity of the materials involved, cleaning and disinfection have to be performed in such a way that no residues of the preparation used remain on the treated surfaces of the instrument. The extremely effective process of thermal sterilization normally used for medical instruments cannot be applied to endoscopes because endoscopes are made partly of temperature-sensitive materials. Another factor to be taken into consideration is that many of the metal parts present are susceptible to corrosion. Finally, endoscopes should be able to be cleaned and disinfected in a short time so that they are always ready in good time for the treatment of the next patient.
While the process of the invention has particular application to endoscopes, the process can be used to clean and sterilize other surgical, medical, or dental devices and equipment, or in fact any equipment or devices having hard surfaces for any use where cleaning and disinfecting such hard surfaces is desired, particularly equipment and devices that cannot tolerate high temperature cleaning and sterilization.
Chlorine Dioxide As Sterilant
Chlorine dioxide is an extremely effective sterilant and bactericide, equal or superior to chlorine on a mass dosage basis. Its efficacy has been well documented in the laboratory, in pilot studies and in full-scale studies. Unlike chlorine, chlorine dioxide does not hydrolyse in water. Therefore, its germicidal activity is relatively constant over a broad pH range.
At pH 6.5, doses of 0.25 mg/l of chlorine dioxide and chlorine produce comparable one minute kill rates for the bacterium Escherichia coli. At pH 8.5, chlorine dioxide maintains the same kill rate, but chlorine requires five times as long. Thus, chlorine dioxide should be considered as a primary sterilant in high pH, lime-softened waters.
Chlorine dioxide has also been shown to be effective in killing other infectious bacteria such as Staphylococcus aureus and Salmonella. Chlorine dioxide is as effective as chlorine in destroying coliform populations and is superior to chlorine in the treatment of commonly found viruses. In a test, Poliovirus 1 and a native coliphage were subjected to these two disinfectants. A 2 mg/l dose of chlorine dioxide produced a much lower survival rate than did a 10 mg/l dose of chlorine.
A sterilant must provide specified levels of microorganism kills or inactivations as measured by reductions of coliforms, heterotrophic plate count organisms and Legionella bacteria. Disinfection is currently defined by the Environmental Protection Agency to mean 99.9 per cent reduction in the Giardia lamblia cyst levels and 99.99 per cent reduction in enteric virus concentrations. Disinfection is expressed as a CT value (i.e. a function of Concentration.times.Contact Time). At the CT values necessary for chlorine dioxide to inactivate 99.9 per cent of Giardia lamblia cysts, the simultaneous inactivation of 99.99 per cent of enteric viruses is also assured.
Activating Acid
Although chloride dioxide has been found to be an excellent sterilant, it is difficult to use in direct form. In gaseous state, chloride dioxide is explosive and poisonous. Accordingly, sodium chlorite is used as a chloride dioxide-liberating material. Chloride dioxide may be liberated from the sodium chlorite (or any other suitable liberating material) by the addition of a suitable activating system, most usually an acid. Various inorganic and organic acids have been tested as activating systems. A description of the various acid systems which may be used is given in EP-A-0176558 (Alcide Corporation). Preferred acids are lactic acid, phosphoric acid, acetic acid, sorbic acid, ascorbic acid, phosphoric acid and hydrochloric acid. It is preferred that the acid should be present in an amount from 0.01 to 10% based on the total weight of the composition. Citric acid is a preferred acid for use in activation. Combinations of suitable acids may be used, e.g. a combination of sorbic, boric and citric acid. Such a combination is preferred as the sorbic and boric acid act not only as activators but also as bactericides in their own right. A higher "kill" is found than if using citric acid alone or in combination with, for example, lactic acid.
Corrosion Inhibition
Many liquid sterilization systems are highly corrosive to metal parts, particularly brass, copper, and aluminium, With long immersion times, even carbon steel and stainless steel could be pitted and sharp cutting edges dulled.
The use of a simple sodium chlorite/acid activator system as a sterilizer of various instruments leads to corrosion of metal parts, due to the aqueous basis of the system. The corrosion means that expensive instruments have a shortened lifetime.
A number of corrosion inhibitors are available and are well-known. However, if an oxidizing agent, for example chlorine dioxide, is to be used as the sterilizing agent, various problems must be overcome in selecting suitable inhibitors. The main problem is that the inhibitors must be effective in powerful oxidizing solutions where chloride ions are present. Furthermore, the inhibitors must be stable under long-term storage in acidic conditions, and must not react together to form deposits or harmful reaction products. The inhibitors should not present a health hazard, either when left in trace quantities on the sterilized instruments or prior to use.
The cleaning environment also produces special problems. The oxygen liberating agent is acidic. Because a number of different metals may be in the sterilizing tank at the same time, galvanic corrosion may be initiated. There is a need to overcome this.
In accordance with the present invention, a new and improved anti-microbial composition is provided which overcomes the over problems. An anti-microbial solution is provided which comprises an oxidizing anti-microbial agent, a copper and brass corrosion inhibitor and buffering agent, a wetting agent and sequestering agent.
The oxidizing anti-microbial agent can be selected from the class consisting of ozone, peracetic acid, organic peroxides, hydrogen peroxides, inorganic peroxides, and other oxygen releasing compounds, chlorine, chlorine dioxide, active chlorine releasing compounds such as chloramines, hypochlorites and phenol.
The copper and brass corrosion inhibitor is selected from the class consisting essentially of triazoles, azoles, benzoates, and five membered ring compounds. Triazoles, particularly benzotriazole and tolytriazole are preferred as being stable in the presence of strong oxidizing compounds. Benzotriazole is most preferred as it also helps to prevent galvanic corrosion in mixed metal systems. Mercaptobenzathiazol might also be utilized but may be destabilized by strong oxidizers. They might be present at 0.01 to 2.0 wt. % of the sterilizer system.
The aluminium and steel corrosion inhibitor and the buffering agent may be selected from the class consisting essentially of chromates, dichromates, borates, nitrates, phosphates, molybdates, vanadates and tungsdates. More specifically to the preferred embodiment, phosphates are preferred of inhibiting steel corrosion and buffering the solution. Molybdates are preferred for inhibiting aluminium corrosion and nitrates, particularly sodium nitrate, for inhibiting steel and ferric corrosion.
The anti-corrosive buffering compounds may include a mixture of phosphate in sufficient volume to produce a final concentration of 1.25 weight per Volume and molybdates in an appropriate amount to produce a final solution of 0.11% weight per volume. Phosphates may also be effective in the range of 0.2% to 12% and the molybdates may be effective from 0.1% to 10%. Optionally, chromates, dichromates, tungstates, vanadates, other borates, and combinations thereof may be substituted in appropriate concentrations to inhibit steel corrosions and aluminium corrosion.
Amines are often used as corrosion inhibitors. However, amine derivatives were rejected because of unpredictable film forming properties.
In hard water, calcium and magnesium salts can precipitate and coat the instruments being sterilized. A sequestering agent appropriate to prevent precipitation, such as sodium hexametaphosphate, may be provided; if deionized or soft water is utilized the sequestering agent may be eliminated. However, to ensure universal applicability with any water that might be utilized, the presence of a sequestering agent is preferred. It has been found that sodium citrate and trisodium phosphate also act as sequestering agents.
A wetting agent present from 0.1 to 100 wt. %, preferably 1.0 to 5.0 wt. %, improves the wetting of the surface of the instrument by the anti-microbial agent. The wetting agent has also been found to increase penetration of the anti-microbial improving anti-microbial efficacy while reducing corrosion. Defoamers and preservatives may also be included at levels of 0.01 to 1 wt. %.